Direct drive for a press

ABSTRACT

The invention relates to a press having an electric direct drive, without any motion transmitting means, such as, for example, gears or gear drives wherein the electric direct drive is located between an eccentric  3  and a connecting rod  6  and brings about a relative movement between the eccentric  3  and the connecting rod  6.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation-in-part application of pending international application PCT/EP2009/054624 filed Apr. 17, 2009 and claiming the priority of German Application No. 10 2008 028 652.4 filed Jun. 18, 2008.

BACKGROUND OF THE INVENTION

The invention resides in a press drive, for example, for the manufacture of metal sheet parts or for the deformation of massive metal components.

In the present state of the art, in the deformation of metal sheets for same time, mechanically driven presses with fly wheel drives have been used. In such presses, the travel-time curve of the plunger as generated by the kinematics of the drive which transmits the drive energy of the fly wheel to the plunger is predetermined. Changes in the travel-drive curve are only possible in connection with a stroke change. The striving for more productive manufacturing processes and the continually increasing requirements in the drawing processes resulted lately in the use of so-called servo presses in the shaping of sheet metal parts.

These servo presses are equipped with variable servo drives capable of generating different press forces. These presses are driven by one or several servomotors, which act directly on the drive train, without a fly wheel and without a clutch. In servo presses with relatively large press forces, high-moment torque motors are often used. With respect to speed and direction of rotation these motors can be controlled in a flexible manner so that they are programmable for different travel-time curves of the plunger. Curves from a sine-shaped course of an eccentric press, the curves of toggle joint lever drives or component design-specific curves may be established. The plunger can be independently position, it can be braked at any location or accelerated and it may even be operated in an oscillating back and forth movement by reversing the eccentric between two points.

Such a servo press is disclosed, for example, in DE 10 2004 009 256 B4. The press described herein includes several servomotors which jointly operate a plunger. The servomotors act on the plunger via a drive which has a mass moment of inertia. This mass moment of inertia may be increased by an additional fly wheel, if desired. However, altogether the resulting mass inertia moment is selected so as to be less than that of conventional presses in which the fly wheel stores sufficient energy to complete a working stroke. It is rather so small that the servomotors can accelerate the fly wheel from a stand still and again brake it to a sand still. With such a design, it is possible to operate the presses on one hand in a reversing operation with variable strokes wherein, on the other hand, high press forces can be obtained with the aid of the fly wheel.

It is, however, a disadvantage of this solution that in spite of drive simplifications, complicated and costly movement transmission means in the form of gears are still needed. DE 41 09 796 C2 discloses an arrangement for pressing, bending and punching of metal work pieces wherein a servomotor acts directly on an eccentric. With this arrangement the stroke length, as well as the press forces, are to be changed a simple manner. In addition, by an axial guiding of the plunger, it's surface of contact with the workpiece is to remain unchanged. A disadvantage of this solution however is surely a limitation to very small press forces. For large deformation presses with several pressure points, such an arrangement is not suitable.

Based on this state of the art, it is the object of the present invention to provide a press drive which on one hand is capable to generate high press forces with a variable plunger movement and, on the other hand is of simple design and cost effective.

SUMMARY OF THE INVENTION

The invention relates to a press having an electric direct drive, without any motion transmitting means, such as, for example, gears or gear drives wherein the electric direct drive is located between an eccentric 3 and a connecting rod 6 and brings about a relative movement between the eccentric 3 and the connecting rod 6.

The basic concept of the invention renders in providing a press with an electric direct drive without motion transmission means as, for example, gears or gear drives. This is achieved in that in an eccentric drive, a direct drive consisting of a rotor and a stator are used which act directly on the, one or several, connecting rods. The direct drive drives directly one or several eccentric or eccentrics which are rotatably connected to the connecting rods. In principle, several variations of the direct press drive according to the invention are possible. In the preferred embodiment of the invention, the electric direct drive is disposed between an eccentric and a connecting rod rotatably supported on the eccentric. The eccentric is provided at its outer circumference with a number of permanent magnets corresponding to a desired press force. At the inner surface of the connecting rod eye facing the permanent magnets—coils are arranged. The operation of the press drive according to the invention corresponds essentially to the mode of operation of a permanent magnet synchronous motor. There is a difference in the mode of operation of the rotor and the stator in relation to the overall system. Which in a conventional permanent magnet synchronous motor the stator is stationary and the motor rotates concentrically around the stator, in the press drive according to the invention also the stator moves relative to the overall system of the press because of the eccentricity of the permanent magnet arrangement relative to the eccentric shaft. However, if the movement of the inner eye surface of the connecting rod relative to the outer surface of the eccentric is considered, the mode of operation corresponds to that of a rotor-stator structure of a permanent magnet synchronous motor.

The connecting rod is rotatably connected to the eccentric preferably via a friction bearing. In this way, it is ensured that between the permanent magnets which are arranged at the outer circumference of the eccentric and the windings which are arranged on the eye surface of the connecting rod on a gap of predetermined size is provided. Only two components of each drive unit are connected with the surrounding structure. The eccentric shaft is rotatably supported at the head end. As bearings common types of bearings known in the art may be used. The second connecting point is at the plunger. It is of a design as it is used in a conventional mechanical press. A bolt which is supported in the center of a connecting rod eye or bore, is rotatably supported at its outer end in the plunger or, respectively, in the pressure point of the plunger. In contrast to the conventional drives the connecting point in the plunger fulfills in the direct press drive according to the invention in addition to the motion on force transmission in the vertical direction also the function of a moment bearing. The drive moment is supported in the plunger bearing via plunger guide structures on the press frame. As a result, a separate moment support structure is not needed in connection with the direct press drive according to the invention.

Further advantages and particulars of the invention will become more readily apparent from the following description of advantageous embodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side view of the press drive according to the invention;

FIG. 1B shows the press drive in an axial cross-sectional view;

FIG. 2 shows the press drive according to the invention in connection with a double toggle joint; and,

FIG. 3 shows the press drive according to the invention with two eccentric drive structures.

DESCRIPTION OF A PARTICULAR EMBODIMENT

FIG. 1A shows a direct press drive 1 according to the invention in a side view and FIG. 1B shows it in an axial cross-sectional view. Shown in the FIGS. 1A and 1B is an eccentric shaft 2 which is rotatably supported in a headpiece which is not shown in the drawings. The eccentric shaft 2 is provided with an eccentric 3 and rotates it about the axis of the eccentric shaft 2. At the outer circumference of the eccentric 3 numerous magnets 4 are securely arranged. In a preferred embodiment the eccentric 3 consists of aluminum. The geometrical shape and the number of the permanent magnets 4 or, respectively, the poles determines the size of the torque that can be generated and of the resulting press force. Opposite the permanent magnets 4 there are windings 5 which are mounted to the inner surface of the eye or opening of the connecting rod 6. Between the outer surface of the permanent magnets 4 and the opposite surface of the windings 5 there is an air gap of generally a few millimeters. When the windings 5 are energized, a circumferentially directed force is generated via the permanent magnets 4 which cause rotation of the inner surface of the connecting rod eye relative to the eccentric 3.

A detailed description of the electromagnetic actions effective between the permanent magnets 4 and the winding 5 is not necessary here since they correspond exactly to the operational principle of permanent magnet synchronous motors which are well known in the art.

The connecting rod 6 and the eccentric 3 are interconnected rotatably by friction bearings 7 as shown in FIG. 1B. At the end of the connecting rod 6 remote from the drive, the connecting rod 6 is provided with a bore 8 in which a bolt 9 is supported by means of a friction bearing 10. This bolt 9 is rotatably connected at its outer ends to the plunger 11. The plunger 11 is guided by the support frame 12 via a linear guide structure (not shown) in such as way that it is movable in vertical direction. When now, the eccentric 3 is isolated by the direct electric drive relative to the connecting rod 6, the plunger 11 is moved vertically because the shaft 2 of the eccentric 3 is rotatably supported at its opposite ends on the head structure of the press frame and the bolt 9 is rotatably connected to the plunger 11.

FIG. 2 shows another embodiment of the press drive according to the invention. The drive arrangement for the connecting rod 13 corresponds to the drive arrangement as shown in FIG. 1. Between an eccentric 14 which is connected to a support shaft 15 and the connecting rod 13 the active elements of the direct drive, here the permanent magnets 16 and the windings 17, are disposed. The permanent magnets 16 are operatively securely arranged on the outer surface of the eccentric 14 proximate the windings 17 mounted at the inner surface of the connecting rod eye. It is noted however, that vice versa, the permanent magnets could be arranged on the connecting rod 13 and the windings 17 on the eccentric. In the exemplary embodiment shown in FIG. 2, an enhanced power drive is provided wherein the driven connecting rod 13 is not directly connected to the plunger 19, but in this case, via a double toggle lever mechanism 18. The double toggle mechanism 18 comprises a left toggle lever mechanism 20 a and a right toggle lever mechanism 20 b. Each of the two toggle lever mechanisms 20 a, 20 b comprises an upper lever 21 a, 21 b and a lower lever 22 a, 22 b. The upper levers 21 a and 21 b are connected to the lower levers 22 a, 22 b via connecting structures 23 a, 23 b. The upper levers 21 a, 21 b are pivotally supported via the pivot joints 24 a, 24 b at a support structure of the frame 25. The lower levers 22 a and 22 b are connected to the plunger 19 at the pivot points 26 a, 26 b. The struts 29 a and 29 b are connected at their ends remote from the drive at the pivot points 27 a, 28 a to left hand (remote) toggle lever mechanism 20 a and at the pivot points 27 b, 28 b to the right hand toggle mechanism 20 b at the end of the connecting rod 13. When now the connecting rod 13 is moved by the driven eccentric 14; that movement is transmitted via the double toggle mechanism 18 to the plunger 19 in such a way that it performs a vertical up and down movement.

FIG. 3 shows another exemplary embodiment of the direct press drive 1 according to the invention. In addition to the drive arrangement already shown in FIG. 1 the two eccentric drive structures shown in FIG. 3 include eccentrics 30 which are linked to the press frame 34 by way of links 32 by means of pivot joints 31 and 33 providing for a kinematics with much increased pressure focus near the bottom dead center position of the plunger structure similar to a toggle lever drive. With this kinematics relatively small drives can be used which provide for relatively large pressure forces where they are needed that is near the bottom dead center position of the drive. The two drives 1 have no mechanical synchronization, for example, in the form of intermediate gears. Synchronization is provided electronically by the control of the electric drive. With such an electronic control, also a tilt movement of the plunger can be obtained by a predetermined unsynchronous drive control. If such a tilt control is used, provisions must be made for the plunger guide structure that parallelity deviations of the plunger can be accommodated.

The press drive 1 of the present invention can be used in connection with single joint or multi-joint drives. The press drive 1 can be combined for follow-up synchronization for module construction with a not over-defined guide structure. The press drive 1 provides a follow-up deviation in the master-slave system which is not over-defined and the joint bolts are used together with one or several guide means at the same time as plunger guides. The press drive 1 may be a triple press with a deep draw arrangement. Preferably the connecting rods 6, 13 of the present invention consist of a fiber-reinforced material.

The invention is not limited to the described exemplary embodiment. It encompasses also all variations within the frame of the inventive concept.

REFERENCE NUMERALS

-   -   1 direct press drive     -   2 eccentric shaft     -   3 eccentric     -   4 permanent magnets     -   5 windings     -   6 connecting rod     -   7 friction bearing     -   8 bore     -   9 bolt     -   10 friction bearing     -   11 plunger     -   12 machine frame     -   13 connecting rod     -   14 eccentric     -   15 support shaft     -   16 permanent magnets     -   17 windings     -   18 double toggle lever joint mechanism     -   19 plunger     -   20 a left hand toggle lever mechanism     -   20 b right hand toggle lever mechanism     -   21 a, b upper lever     -   22 a, b lower lever     -   23 a, b connecting structure     -   24 a, b pivot joints     -   25 head piece, frame     -   26 a, b pivot points     -   27 a, b pivot points     -   28 a, b pivot points     -   29 a, b struts     -   30 eccentric     -   31 pivot joints     -   32 links     -   33 pivot joints     -   34 head piece, frame 

1. A press comprising a press drive (1) including at least one eccentric (3, 30) and at least one connecting rod (6) each connected to an eccentric to be activated thereby, each eccentric being operated by a direct electric drive, said direct electric drive being formed between the eccentric (3) and the connecting rod (6) connected to the particular eccentric for generating relative rotational movement between the eccentric (3) and the connecting rod (6).
 2. The press according to claim 1, wherein permanent magnets (4) are disposed on one of the eccentric (3) and the connecting rod (6) and windings (5) are disposed on the connecting rod (6) or, respectively, eccentric (3) for generating the relative rotation between the eccentric (3) and the connecting rod (6).
 3. The press according to claim 1, wherein the direct electric drive (1) is a permanent magnet synchronous drive.
 4. The press according to claim 4, wherein the direct electric drive (1) is an enhanced-power drive.
 5. The press according to claim 1, wherein the connecting rod (6) is rotatably connected with its end remote from the drive (1) to a plunger (11) via a bearing (10) which also provides for reaction torque support of the press drive (1).
 6. The press according to claim 1, wherein the eccentric (3) is firmly connected to an eccentric support shaft (2) which is rotatably supported on a frame head piece (25).
 7. The press according to claim 1, wherein several directed press drives (1) are provided which act on a plunger (11).
 8. The press according to claim 1, wherein the movement and force transfer of the connecting rod (6) to the plunger (11) occurs by means of a lever arrangement.
 9. The press according to claim 8, wherein the movement and force transfer lever arrangement is a toggle lever mechanism (18).
 10. The press according to claim 1, wherein said press drive (1) being useable in connection with single joint or multi-joint drives.
 11. The press according to claim 1, wherein the press drive (1) is combined for follow-up synchronization for module construction with a not over-defined guide structure.
 12. The press according to claim 1, wherein a follow-up deviation in a master-slave system is not over-defined and the joint bolts are used together with one or several guide means at the same time as plunger guides.
 13. The press according to claim 1, wherein the press drive (1) is a triple press with a deep draw arrangement.
 14. The press according to claim 1, wherein the connecting rod (6) consists of a fiber-reinforced material. 